National Australia Bank has written off two remaining synthetic collateralised debt obligations in its Specialised Group Assets portfolio.NAB announced yesterday that it had "taken action to remove the economic risk of the SCDOs", which had a face value of A$600 million.As a result of the decision, NAB's risk-weighted assets have been reduced by $1.5 billion.In 2009, in response to the financial crisis, NAB created a $24 billion portfolio of Specialised Group Assets (of which $17 billion was drawn) and started running them off. These "non-franchise" assets included $9 billion of conduit transactions, $8 billion of corporate loans, $3 billion of leveraged loans, $2 billion of project finance and $1 billion of credit wrapped bonds.Prior to their transfer to the SGA portfolio, $13 billion of these credit risk-weighted assets were managed by the bank's nabCapital division in the United Kingdom, $7 billion were sourced from the United States and the balance were from Australia.The SCDOs were part of a nabCapital securitisation portfolio.NAB said yesterday that a $160 million provision associated with these assets had been used to absorb costs.In its 2010/11 financial report, NAB reported that the risk-weighted assets in its Specialised Group Assets portfolio were down to $15 billion.